#define _CRT_SECURE_NO_WARNINGS
class Solution {
public:
    int waysToStep(int n) {
        vector<int> dp(n + 1);
        int MOD = 1e9 + 7;
        if (n == 1) return 1;
        if (n == 2) return 2;
        if (n == 3) return 4;
        dp[0] = 0;
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 4;
        for (int i = 4; i <= n; i++)
        {
            dp[i] = ((dp[i - 1] + dp[i - 2]) % MOD + dp[i - 3]) % MOD;
        }
        return dp[n];

    }
};